Over the course of his 17-year major league career, Lefty Grove led the American League in ERA nine times, with a career single-season low of 2.06 for the 1931 Philadelphia Athletics.[6]Roger Clemens has won the second-most ERA titles, capturing six in the American League and one in the National League.[7]Sandy Koufax led the National League in ERA for five consecutive seasons (1962–1966); Koufax' five awards are the most won consecutively by any player and are tied for the most awards by a player in the National League with Christy Mathewson and Clayton Kershaw.[8][9][10] In the American League, Walter Johnson also won five ERA titles,[11] and Pedro Martínez has won a total of five (four American League and one National League) with two different teams.[12]

The lowest single-season ERA in league history was posted by Tim Keefe, whose 0.86 ERA in 105 innings pitched for the National League's Troy Trojans in 1880 led his closest competitor by .52 runs.[13] In the American League, Dutch Leonard's 0.96 ERA is a single-season record.[14] Keefe and Leonard are the only two pitchers ever to allow less than one run per nine innings pitched in a single season. The widest margin of victory for an ERA champion is 1.96 runs, achieved when Martínez' 1.74 ERA led Clemens' 3.70 in the American League during the 2000 season. The largest margin of victory in the National League is 1.26 runs—Dazzy Vance's 2.61 ERA over Carl Hubbell's 3.87 in 1930. The smallest margin of victory for an ERA champion is .009 runs. Although the statistic is traditionally recorded to two decimal places by most sources,[15][16][17] the 1988 American League title was decided by a margin of less than one hundredth of a run when Allan Anderson's ERA of 2.446 (55 earned runs in ​2021⁄3 innings)[18] bested Teddy Higuera's 2.455 mark (62 earned runs in ​2271⁄3 innings).[19] Other contests decided by one hundredth or less include Luis Tiant's 1.91 ERA ahead of Gaylord Perry's 1.92 in 1972[20][21] and Mark Fidrych (2.34) over Vida Blue (2.35) in 1976.[22][23]

a While Baseball-Reference.com lists both Scarborough and Hall of Famer Bob Lemon with an ERA of 2.82 in 1948, Scarborough's average is lower (2.817) than Lemon's (2.820) if extended to three decimal places.

bc While Baseball-Reference lists both Anderson and Higuera with an ERA of 2.45 in 1988, Anderson's average is lower (2.446) than Higuera's (2.455) if extended to three decimal places.

d Until 1981, the rules stated that the number of innings pitched should be rounded to the nearest whole inning. This explains why McCatty was, at the time, awarded the 1981 ERA title although his ERA appears to be slightly higher than that of Stewart.[291]